SAN FRANCISCO — On the eighth day of her son’s life, Julia Query welcomed friends and family to celebrate his birth and honor their Jewish heritage.

But there was no crying, no scalpel, no blood, no “mohel” — the person who traditionally performs ritual circumcisions in the Jewish faith. Elijah Rose’s “bris” differed markedly from the ceremony long used to initiate Jewish boys into a covenant with God: There was no circumcision.

“I knew before I was even pregnant that I would not circumcise,” said Ms. Query, 39, a San Francisco filmmaker whose son was born in 2002. “It’s not like you’re just cutting a piece of paper off a pad — there’s no ‘cut here’ line. It’s not made to be cut off, and I would never, ever do that to my baby.”

Ms. Query is among a growing number of American parents refusing circumcision. According to a study by the National Health and Social Life Survey, the U.S. circumcision rate peaked at nearly 90% in the early 1960s but began dropping in the ’70s. By 2004, the most recent year for which government figures are available, about 57% of all male newborns delivered in hospitals were circumcised. In some states, the rate is well below 50%.

Experts say immigration patterns play the biggest role in the decline, which is steepest in Western states with big populations from Asian and Latin American countries where circumcision is uncommon. The trend has also accompanied a change in Americans’ attitudes toward medicine and their bodies.

“The rates of drug-free labor and breast-feeding all rose during the 1980s, while the initial declines in male circumcision rates began during the 1980s as well,” said Katharine Barrett, an anthropology lecturer at Stanford University. “It may have been part and parcel of the wider effort to reclaim bodies — adult female and infant male — from unnecessary and potentially harmful medical interventions.”

Circumcision remains the nation’s most common surgery, and America is still one of the few developed countries where a majority of baby boys are circumcised. Many doctors still recommend circumcision because of some evidence that it reduces the risk of penile cancer, urinary tract infections, and perhaps sexual transmitted diseases.

Many major insurance companies still cover it, and many hospitals offer it free for newborns. Since 1999, the American Academy of Pediatrics has not endorsed routine circumcision.

About one in three males worldwide is circumcised. In America, the rates vary widely by region. It is most prevalent in the upper Midwest.

In 2004, according to data compiled by the federal Agency for Healthcare Research and Quality, more than 79% of newborn boys in the Midwest were circumcised before leaving the hospital. Michigan and Kentucky had the highest rates, at 85%.

In the fast-growing West, the rate declined dramatically — from 64% in 1979 to just under 32% in 2004. In California, the rate of hospital circumcisions among newborns was 21%. California — which has more immigrants than any other state — had the lowest circumcision rate in the study, which had comprehensive data on only 27 states. The decline coincides with rising immigration from Asia and Latin America.